Position Measuring Device Moiré Torsion Error Reduction
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Solution Overview
Problem
Existing position measuring devices face errors due to Moiré twisting when the scanning unit and scale rotate, particularly in high-resolution measurements, as existing arrangements are either inefficient or prone to measurement inaccuracies if one incremental graduation track becomes dirty.
Innovation Solution
A position measuring device with two incremental graduation tracks parallel to the measuring direction and a reference marking track, where the incremental and reference pulse signals are generated using separate scanning means, ensuring the same neutral Moiré axis to prevent errors from rotation and maintaining signal reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference markings are arranged laterally adjacent to the incremental graduation track, then reference pulse signals can be generated, but position determination errors occur due to Moiré rotation
Solution Approach 1:
The patent applies asymmetry by arranging the reference marking track and incremental graduation tracks in a specific asymmetric configuration where the reference marking is positioned between two incremental graduation tracks. This asymmetric arrangement ensures that the neutral Moiré axis passes through the reference marking, making the reference pulse signal generation insensitive to Moiré rotation effects that would otherwise cause position determination errors.
Solution Approach 2:
The patent transitions from a single incremental graduation track to a configuration with two incremental graduation tracks positioned on opposite sides of the reference marking track. This dimensional change in the arrangement allows for separate scanning of the incremental tracks while maintaining a common neutral Moiré axis, thereby eliminating the position determination errors caused by Moiré rotation.
2Measurement precision
If two incremental graduation tracks are arranged on both sides of a reference marking, then Moiré distortion errors are minimized, but device complexity and cost increase
Solution Approach 1:
The patent merges the scanning functions by using a single scanning unit that simultaneously scans both incremental graduation tracks and the reference marking track. The scanning unit is configured with scanning beams that can detect signals from all three tracks, thereby reducing device complexity while maintaining the benefits of having two incremental tracks for Moiré distortion compensation.
Solution Approach 2:
The scanning unit is designed with multi-functionality to perform multiple tasks: it scans the reference marking to generate reference pulse signals, scans the first incremental graduation track to generate first incremental signals, and scans the second incremental graduation track to generate second incremental signals. This universal scanning capability eliminates the need for separate scanning systems, thereby reducing device complexity and cost.
3Reliability
If separate scanning means are used for reference pulse signals and incremental signals, then measurement reliability is improved, but device complexity increases
Solution Approach 1:
The patent segments the scanning function into distinct scanning beams: a first scanning beam is dedicated to scanning the reference marking track for generating reference pulse signals, while second scanning beams are dedicated to scanning the incremental graduation tracks for generating incremental signals. This segmentation ensures that reference pulse generation and incremental signal generation are performed by separate scanning means, improving measurement reliability while maintaining a unified scanning unit structure.
4Measurement precision
If one incremental graduation track becomes dirty, then measurement accuracy deteriorates, but using two tracks increases redundancy
Solution Approach 1:
The patent applies local quality by having two separate incremental graduation tracks that can be independently scanned. If one track becomes dirty or contaminated, the other track remains clean and functional, allowing the system to continue accurate measurements. The scanning unit can selectively use the clean track, thereby maintaining measurement precision and reliability even in the presence of localized contamination.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures accurate position determination and stable incremental signal amplitudes even under severe Moiré torsion, enhancing the reliability of position measurements by maintaining the correct assignment of reference pulse signals to incremental signals.
Implementation Method 1
each of the incremental graduations being exposed to a scanning beam of rays at least once in an incremental signal scanning field to generate the incremental signals
Implementation Method 2
The scanning unit comprises first scanning means for generating the reference pulse signal
Data Source
Figure 1a
Figure 1b
Figure 1c
AI summary
A position measuring device is described, comprising a scanning unit and a scale that is movable in at least one measuring direction. In one variant, the scale comprises two incremental graduation tracks extending parallel in the measuring direction, between which is a reference marking track with at least one reference mark at a reference position. The scanning unit comprises first scanning means for generating the reference pulse signal and second scanning means for generating the incremental signals, wherein, for generating the incremental signals, each of the incremental graduations is illuminated at least once in an incremental signal scanning field by a scanning beam. In another variant, the scale comprises two reference marking tracks extending parallel in the measuring direction, each of which has reference marks at at least one reference position that are symmetrically arranged about an axis in the measuring direction.An incremental division track is arranged between the reference marker tracks. The scanning unit comprises first scanning means for generating the reference pulse signal and second scanning means for generating the incremental signals. To generate the reference pulse signal and the incremental signals, the reference markers are stimulated at least once in each reference pulse signal scanning field by a scanning beam, and the incremental division is stimulated at least once in each of two incremental signal scanning fields by a scanning beam (Fig. 2b).